It is commonly known that different kinds of furnaces may be used to process substrates such as substantially circular wafers for integrated circuit processing. A first kind of furnace comprises a horizontal furnace having a process chamber that substantially extends in a horizontal direction. To process said circular wafers, the wafers are loaded into the process chamber such that the respective wafers are oriented substantially vertically and arranged substantially parallel. Another kind of furnace comprises a vertical furnace with a process chamber arranged in said furnace such that a central axis of the process chamber substantially coincides, or at least extends in a substantially similar direction, with a central axis of the vertical furnace. Before processing wafers in a vertical furnace, the wafers are provided in a loading configuration wherein the wafers are substantially horizontally oriented and are mutually spaced in a vertical direction wherein the centre points of the wafers are approximately positioned on the central axis of the process chamber. Vertical furnaces usually have a load size of 100-150 wafers that are spaced apart such that during processing of the respective wafers the entire surface of each substrate can be subjected to the process. In order to enable the substrate to be exposed to one or more volatile precursors, which may react and/or decompose on the substrate surface to produce a desired thin film, a certain minimal space needs to be available between adjacent substrates. Consequently, the load size of vertical furnaces is limited and determined by the size of the respective furnace and kind of process used to apply a thin film on the wafers provided in said furnace. At the same time, a vertical furnace can be automated more easily than a horizontal furnace.
Due to increasing demand of thin semiconductor substrates such as solar cells, it is desired to enhance the throughput of substrates to be processed in such a vertical furnace. Therefore, it is an object of the present invention to provide for an improved method to process planar thin semiconductor substrates such as solar cells in a known furnace. More in particular an object of the invention is to provide a method to process solar cells in a vertical furnace with an increased throughput.